We plan to define the cystic fibrosis (CF) gene(s) by the use of polymorphic DNA markers (RFLPs) in genetic linkage studies. We have identified one such marker (DOCRI-917) genetically linked to a cystic fibrosis locus at a distance of 15 centimorgans (cM) (about 15 million nucleotide basepairs). We plan to 1) expand the informativeness (i.e. the polymorphism) at or near the existing marker, DOCRI-917, and to physically map the locus and thereby the CF gene itself, 2) to identify additional DNA polymorphisms closer and flanking the CF locus by the construction of a genetic linkage map of the chromosome on which the CF locus resides using the set of over 500 polymorphic DNA probes we have already identified as well as new chromosome specific probes we plan to isolate, 3) to investigate the possibility of genetic heterogeneity of CF, i.e. determine the number of genes which, when homozygous, cause the disease by analysis of a larger set of CF families and 4) if definitive evidence is found for additional CF genes, we plan to use our large set of polymorphic probes to detect linkage to these additional genes. These studies will open the way for all types of molecular approaches leading to more narrowly defining the chromosomal locus for CF. This will eventually lead to identification of the CF gene(s) and the molecular defect(s) responsible for the disease. An application of these studies will be the development of presymptomatic diagnostic tests for cystic fibrosis.